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Thursday, February 20, 2014

In my post a
couple of weeks ago on the selection of NASA’s next low cost planetary
mission, I said that the conditions NASA imposed on scientists proposing
missions would determine much of what kind of missions scientists could impose.

NASA will accept proposals to study any solar system body except the sun and the Earth. Scientists cannot propose missions to study planetary systems around other stars (NASA astrophysics program funds these missions.)

NASA announced that the budget for the spacecraft, instruments, and
data analysis (the Principal Investigator (PI) budget) would be $450M (FY15
dollars). This is a small increase from
the last competition’s PI budget of $425M, and by itself would not keep up with
inflation.

Outside of the PI’s budget, NASA will pay for the cost of the mission
launch. For the first time, NASA will
pay for the cost of the mission’s operation outside of the PI budget. In past competitions, missions with long
flight times, and hence high operations costs, were at a disadvantage to
missions with low operations costs. This
appears to be an effort to equalize operations costs. Missions that would benefit are any with
flight times of several years compared to the weeks or months to reach Venus,
the moon, or Mars. With operations costs
not counted against the PI’s budget, the new competition probably keeps up with
inflation compared to the previous competition.
(NASA’s announcement does emphasize that the operations costs projected
for a mission must be ‘reasonable’.)

The major limitation for this competition is that NASA will not provide
a radioisotope power system for this competition. While recent NASA presentations suggests it
has sufficient plutonium-238 fuel to support a Discovery mission, that fuel
could not be prepared in time to meet the expect launch date for this
competition. As a result, any mission
that cannot use solar power is effectively eliminated. This would include missions beyond Jupiter,
to the permanently shadowed lunar polar craters, or where large solar panels
just won’t work like for a mission that would make multiple landings on a comet
(see this description
of the CHOPPER mission proposed for the last competition).

NASA traditionally offers scientists various technologies at the space
agency’s cost that it would like to see tested in space. For this competition, NASA says it is
considering providing a version of the NASA Evolutionary Xenon Thruster (NEXT)
ion propulsion engine as well as heat shield technology for missions that would
send a probe into planetary atmosphere.
These former would benefit missions that would require large amounts of
thrust such as main belt asteroid missions or comet rendezvous missions. The latter would benefit missions such as
Venus atmospheric probes.

NASA also is considering requiring proposals to include carrying its
Deep Space Laser Communications (DSLO) package.
This technology was tested on the LADEE mission currently orbiting the
moon and showed that lasers could return much larger volumes of data than
traditional radio systems. NASA would
now like to try this technology from a spacecraft in deep space. Missions with low data rates such as Venus
atmospheric probes probably would see little benefit from the DSLO system. Missions with lots of imaging data such as Venus
radar mappers or Io multi-flyby missions would make good use of the DSLO
system.

One other new requirement is a limitation on how much of the cost of
instruments foreign space agencies can contribute. NASA has had a limitation that foreign
governments could not contribute more than one-third the cost of the total
mission. That cap now also applies to
the contribution to the cost of the science payload, too. This appears to be a way of preventing a
proposal team from minimizing its PI costs by filling most of the payload with
instruments paid for by other governments.
NASA apparently wants US planetary missions to provide opportunities for
US scientists to fly their instruments.

All in all, this looks to be a nice opportunity that keeps the
Discovery program on track to continue to support innovative missions to a
variety of destinations in the solar system.

Key dates (subject to change)

May 2014 – release of draft Announcement of Opportunity with details
for proposers

Tuesday, February 18, 2014

Imagine flying deep within the asteroid belt to study the most
unreachable location in the solar system: the deep core of a terrestrial world.

That will be one asteroid mission that will be proposed for NASA’s
upcoming competition to select its next Discovery mission to explore the solar
system.

We know nothing about what the geology of metal world would be like. Could the impact crater look like frozen splats? Credit: JPL/Corby Waste

Asteroids are found scattered across the solar system like artifacts
strewn across an archaeological site.
Just as a delicate gold necklace and simple rough potsherd can speak the
different strata of an ancient society, the many types of asteroids speak of
the strata of conditions in the earliest eon of the solar system. Stony bodies, for example, formed closer to
the sun while icy bodies formed further away.

By studying asteroids (and their cousins, the comets), scientists can
study the remains of conditions from the earliest solar system.

Most asteroids are smallish affairs with diameters measured in meters
to kilometers or at most a few tens of kilometers and are usually chips knocked
from larger protoplanets by impacts from still other asteroids. In a few cases, though, the original protoplanets
remain largely intact. By studying these
worlds with spacecraft, geologists can examine how the terrestrial planets
formed. On the true planets, that early history
is long lost because of geologic activity.

Some of the protoplanets have a familiar structure like Vesta with its
rocky mantle and metallic core that resembles the structure of the terrestrial
planets. Others are unlike any world we
have explored to date. Massive Ceres is
a rock-ice world with a deep mantle of ice and is a member of a family of
asteroids that emit water vapor (some are even comet like with full dust and
ice vapor trails). The asteroid Psyche
is a metal world that may be the remnant core of protoplanet.

(When I first began reading about the solar system several decades ago,
comets were icy balls with some dust and asteroids were rocky. Now we know that comets and asteroids are a
continuum and many asteroids contain substantial amounts of ice that would have
been water when these bodies still retained the heat form their formation.)

Asteroids have been popular targets for solar system missions. NASA has flown two asteroid missions and is
building a third with a fourth listed as high priority. Japan’s JAXA space agency has flown one
mission, is building a second, and is planning for a third. American and European scientists have
proposed numerous additional missions.
In the last competition for NASA’s low-cost Discovery program (~$425M
missions), over a quarter of the 28 missions proposed would have flown to an
asteroid or observed them with a space telescope.

In the competition for the next Discovery mission expected to begin
this year, we can expect a similar enthusiasm from the scientific
community. A good portion of the
proposals will probably be to fly to one or more of the small asteroids whose orbits
are near the Earth’s. Flights to these
worlds are relatively easy, making the missions that orbit them and even land budget
bargains and low risk. In addition,
collisions, gravitational influences of the true planets (especially Jupiter),
and even the pressure of the sun’s light have scattered the smaller asteroids
across the solar system. Within easy reach from Earth are bodies representing a
plethora of conditions that were found across the early solar system.

Scientists who want to study protoplanets have to look to the asteroid
belt between Mars and Jupiter. There
the Discovery Dawn spacecraft has finished its studies of the rocky protoplanet
Vesta and is headed towards the rock-ice dwarf planet Ceres.

While the Dawn mission picked off two of the most exciting protoplanets,
there are plenty more. European
scientists in their last mission competition proposed two main belt asteroid
missions (neither selected). They
focused on two classes of asteroids. The
first were asteroids that have been observed to eject jets of water vapor. The second class was actually a single
asteroid – the metal world Psyche.

Scientists planning to propose Discovery missions usually are reluctant
to say much about their ideas. The
competition is tough and missions usually are proposed several times. Why say something that would give a competing
team a good idea? So of the eight
asteroid Discovery missions proposed last time, we know very little about what
was actually proposed.

Even with the stiff competition, though, some scientists try to build
support for their proposals by making some disclosures in public. It can’t hurt to have the members of the
review panels already excited by a mission before they evaluate the proposal. In general, we hear more about how
scientifically interesting a destination is (those facts are widely known) and
less about the spacecraft and instruments (what I know many of the readers of
this blog are most interested in). The
few times we hear about detailed implementation, it generally is to a
destination that seems beyond the reach of a Discovery-class mission where
building technical credibility before the review likely helps. All three of the teams that have proposed
missions to the Saturn system, for example, have revealed a fair amount about
the implementation.

The team preparing to propose a mission to the metal world Psyche has
been relatively open about their proposal although they talk more about the
destination than their spacecraft and instruments.

The
asteroid Psyche is one of the larger asteroids.
Credit: Lindy T. Elkins-Tanton

Fortunately, the destination is worth learning about. Stop for a second and ask yourself – what
location for all the planets do we know least about?

It’s the cores of the planets.
We can infer much about the size of the cores from seismic data (so far
available only for the Earth and the moon but soon also for Mars),
gravitational studies that reveal the mass of the core, and measurements of the
magnetic field when present. No one,
though, has ever seen a planetary core or directly measured its composition.

The asteroid Psyche may give us that opportunity. As bodies coalesced in the early solar
system, initially random chance brought dust and ice to clump together. Once a body reach a kilometer or more in
diameter (what is called a planetesimal), its gravity became strong enough to
pull more material in to it. At a
critical size, the heat from radioactive elements, collisions, and
gravitational pressure melted the interiors of these worlds and they became
protoplanets. Iron and nickel metals sank to the cores, mantles formed from the
lighter silicate materials or ices, and a crust may have formed of either
unmelted primitive materials, or by volcanism from the interior flooding the
surface.

Three possible origins have been suggested for the metallic asteroid Psyche
(~250 km diameter), all of them intriguing.

Psyche could be an asteroid in which repeated collisions chipped off
the crust and mantle, leaving the core a naked body. If this is the case, then a mission to this
world would be the equivalent to a mission deep below the surface of any of the
terrestrial planets to examine their cores. It’s a journey that is possible only because
chance created and then preserved from ultimate destruction by further
collisions Psyche’s naked core.

Psyche could be the remnant of the collision of two protoplanets that
shattered and expelled the core of the smaller body to become Psyche. In this case, we wouldn’t get to examine an
intact protoplanet’s core. We’d still
get to examine the composition of a protoplanet’s core, though, and also see
how a world composed almost purely of metal formed itself following a collision. Collisions such as this would be been common
in the early solar system. One is
believed to have created the Earth-moon system. All planetary cores, in fact,
almost certainly formed from multiple generations of fragmentation,
differentiation, and merging of previous cores.

And finally, Psyche could have formed so close to the early sun that all
materials other than metals (and some silicates) would have been evaporated and
have been unavailable for planet building.
Later migrations of Jupiter and Saturn in and out of the inner solar
system could have moved this world to its present location in the asteroid
belt. In this case, a mission to Psyche
would show us an entirely new class of world.

Telescopic observations reveal that Psyche’s surface is 90% metallic
and 10% silicate rock. A spacecraft
orbiting Psyche likely could distinguish between these scenarios by measuring
the composition in detail and looking at the arrangement of the silicate
material. If the silicate material is
primarily high-magnesian pyroxene or olivine, then these silicates are likely
the remnants of a crystallizing magma ocean, and indicate that Psyche started
as a differentiated planetesimal and had its mantle stripped, validating the
mission’s prime hypothesis for this body. If the silicates are all primitive
chondritic material, then they were likely added as later impacts, and Psyche
may have started life as a highly reduced metallic body without a significant
silicate mantle, or, the nature of impact flux and its consequences are far
more significant than our current models indicate. The numbers and shapes of
craters on Psyche’s surface may help decipher that story.

Here are some of the key questions a spacecraft would explore at
Psyche: How did this large metal world
form? If it is a remnant core, what is
the composition and structure of a terrestrial world’s core? If Psyche was once molten, did it solidify
from the inside out, or the outside in? We
have a number of meteorites from a single metallic asteroid (the group IVA iron
meteorites); is Psyche their source? The
metallic asteroids appear to be much less dense than the metallic meteorites;
are these asteroids rubble piles?

We know a great deal about the geology and surface features of rocky
worlds, icy worlds, and will learn about rock-ice worlds when the Dawn
spacecraft reaches Ceres next year. Metal worlds may differ significantly in
their appearance. What does the surface of a metal world look like? Imagine how strange a crater might appear.
Laboratory tests of craters in metal show that sometimes the ejecta flaps
freeze before they fall; could this happen on a planetesimal?

Like the Dawn spacecraft, the Psyche spacecraft would use solar
electric propulsion. As for instruments,
the proposal team’s Principal Investigator, Dr. Lindy T. Elkins-Tanton of the
Carnegie Institution for Science, told
me, “We hope to learn not just about the surface of this metal body, but also
about its interior, which requires geophysics. We'll be carrying a
magnetometer, and we'll use the spacecraft itself to develop a detailed model
of the body's gravity field. With these measurements and knowledge of
topography, we'll get information on internal structure.

“We'll have an imager, of course, in the hopes of seeing some
unforeseen new metal geology, and to count craters to measure the age of the
surface, among other goals. Measuring the surface compositions of a metal
object remotely is more difficult. Infrared spectrometers are great for
silicates, but only gamma ray spectrometers can measure metal composition. We
expect, though, to see some silicate materials along with the metals.”

I asked Dr. Elkins-Tanton about the possibility of flying to a second asteroid. She told me that they looked at this and concluded
that it wasn’t feasible. No other
asteroid visit would address their questions about metallic asteroids (and the
instrument suite that would be wanted for a comet-like asteroid, for example,
would be different). It also would be
difficult to fit second asteroid visit into a Discovery mission budget.

In my previous post, I wrote that Discovery mission competitions
surprise and delight us with the cleverness of the missions proposed. While we will hear little about many of the
missions likely to be proposed for the asteroids, the Psyche mission gives an
idea of what is possible.

You can read a two page summary of the science goals for the Psyche mission
at this link.

My thanks to Dr. Lindy Elkins-Tanton for reading a draft of this post and making several useful suggestions.

Wednesday, February 5, 2014

The Discovery program is unique in NASA’s planetary program. Within the budget constraints of each
selection, the scientific community is free to propose any mission to any
destination. In the last selection, the
finalists were the Insight Mars geophysical station (which was selected), a
mission to land on the lakes of Titan (TiME), and a mission to orbit and
repeatedly land on the nucleus of a comet (CHOPPER). To paraphrase Forest Gump, the Discovery
program is like a box of chocolates – you never know what you’re going to
get. The creativity of the scientific
community has given us a wide assortment of missions in the past and is likely
to surprise and delight us again.

The missions of the Discovery program have visited a wide-range of solar system destinations. Image from Historic Spacecraft and used under a creative commons license.

A month so or so ago, it appeared that the selection of NASA’s next
mission in this, its lowest cost planetary mission program, was on indefinite
hold.This program in its first decade
produced an incredible wealth of missions of ten missions that studied Mercury,
the moon, Mars, asteroids, comets, and the sun.The program more than fulfilled its goal of ensuring that NASA’s
planetary mission portfolio was diversified.

In the second decade, though, just two missions were approved, to the
moon and Mars. For the next decade it
was uncertain when the next mission selection would begin. It appeared that already approved missions in
development would consume most of the foreseeable mission development budget.

That has changed with the NASA
budget that was just approved.
Congress directed NASA to accelerate the selection of the next,
thirteenth Discovery mission. Based on
the proposals from the last Discovery mission (see list at the end), we can
expect a good deal of creativity from the scientific community.

By contrast, the New Frontiers program ($750M to $1B missions) has a
list of pre-selected, high priority missions (although creative solutions can
be proposed). The other class of
missions, Flagship missions ($1.5B+) like Cassini or Curiosity, are selected by
panels of scientists and fostered and developed over a decade or two. The next two likely missions in this class,
the 2020 Mars rover (already approved) and a Europa multi-flyby spacecraft (in
study), are well known.

Realistically, there will be limits to the missions that can be
proposed for the next Discovery mission.
NASA’s managers will have to decide on the budget they can afford for
the mission. In the past, scientists
could propose missions with a total cost of ~$425M for the spacecraft, its
operation, and the data analysis. (NASA
paid for the cost of the launch and some other expenses separately.) Jim Green, head of NASA’s planetary program,
said in a meeting recently that the budget will decide how ambitious missions
could be. To afford a mission to the
outer solar system, the budget would need to be closer to $500M, but a smaller
budget could be set for missions to the moon, Venus, or Mars.

There also will be other key programmatic decisions. Will NASA pick up the costs of providing a
plutonium power system to enable missions that can’t use solar panels for power
such as spacecraft that would travel to Saturn, the permanently shadowed
craters of the moon, or land repeatedly on a comet? The latest count of available plutonium power
systems suggests that one will be available for either a Discovery or a New
Frontiers mission this decade.

A fixed budget also puts missions with long flights to their
destinations at a disadvantage compared to missions that go to worlds next door. Each year of flight to reach a destination
costs the mission $7M to $10M, a big disadvantage if the voyage takes five to
seven years. The scientific community
has proposed that NASA allow the budget to be flexible to cover costs of long
flights.

Then there’s a question of how much risk NASA is willing to
accept. The more ambitious the proposal,
the greater the chance it would bust its development budget or fail sometime
after launch. Commentators have said
that NASA appears to have become risk adverse in its Discovery mission
selections (see here). On the other hand, where NASA once had the
budget to select two missions every two years, it now is looking at perhaps
just two Discovery missions a decade.
The relative cost of failure has grown, and low-risk, good-science
missions have been available to select.

We will get answers to most of these questions (except the tolerance
for risk) in a few months when NASA releases the draft Announcement of
Opportunity (AO) for the next selection.
AO’s spell out what NASA is looking for, the budget it has set, the
class of launch vehicles it will pay for, and what resources it will make
available such as a plutonium power supply.
Proposers will decide to propose or not in response to the constraints
placed on the selection.

Congress asked that the AO be released this May, but NASA’s managers
have said that they and the scientific community couldn’t be ready by that
date. Instead, a draft AO will come out
for the community to comment on in the next few months. NASA has said that the final AO will be
released before next October.

Once the final AO is released, we will still need patience to wait to
find out which mission is selected and even longer to see it reach its
destination. The previous AO was
released in June 2010, the three finalists were selected in May 2011, the
winning InSight mission was selected in August 2012, and launch will come in
2016. If the next selection follows the
same pace and the AO is released in, say, September 2014, the finalists may be
known in August 2015, the winner selected in November 2016, and launch in
2020. If the mission goes to Venus, the
moon, or Mars, it could arrive at its destination in weeks or months. If it goes to Saturn, it could take seven
years.

There’s also a question of how NASA will fit this mission into its
budget, which is already largely spoken for by missions in development. NASA had planned to release the AO for its
next New Frontiers mission in 2015. Will
that be delayed or does NASA think it can select two new missions this decade? We will know more when NASA’s proposed 2015
budget is released in March.

In the hopes that future budgets will support the selection and
development of the next Discovery mission, this is the kick off post for what
will be a semi-regular series of posts on missions that are likely to be
proposed.

I’ll close with a list of previous Discovery mission selections and
what’s known about the list of missions that were proposed for the last
selection. This will give an idea of the
range of creative missions that may be proposed for the next selection.

Selected DISCOVERY and Mars Scout missions

The Mars Scout program selected missions similar is scope to the
Discovery program and has since been merged with the Discovery program. I’ve indicated these missions with an asterisk.

The first two missions were selected by NASA without an AO

NEAR – near Earth asteroid rendezvous and landing

Pathfinder – Mars lander and rover

AO Date and Missions

1994: Lunar Prospector -
orbiter

1994: Stardust comet sample
return and 2 comet flybys

1996: Genesis – returned samples
of the solar wind

1996: CONTOUR – multiple comet
flybys (failed)

1998: Deep Impact – Delivered impactor
to comet & 2 comet flybys

1998: MESSENGER – Mercury orbiter

2000: Kepler – exoplanet hunter

2000: Dawn – orbit asteroids
Vesta and Ceres

2002: *Phoenix – Mars polar
lander

2006: GRAIL – 2 lunar orbiters

2006: *MAVEN – Mars orbiter

2010: InSight – Mars geophysical
station

Proposals in response to the 2010 AO

NASA does not release any information on missions proposed except for
the three finalists (and then only limited information except for the
winner). The competition is tough and
most scientists propose multiple times, so most want to keep their proposals as
confidential as possible. NASA did
release the number of proposals for each class of destination. Where I can, I’ve listed additional detail
based on what proposers stated publicly and based on a list maintained by Blackstar
at the NASASpaceflight.com forum.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.